One of the most challenging aspects of today's energy technologies is to effectively convert waste heat from a combustion process of an internal combustion engine into useable power. Such power can be in the form of electrical or mechanical power for use in stationary and/or mobile applications.
Methods of converting waste heat into useful forms of energy are commonly referred to as bottoming cycles. Systems that utilize a bottoming cycle to provide power are referred to herein as bottoming cycle power systems.
Systems that utilize a fuel combustion process in an internal combustion engine (such as a piston engine or a turbine engine) as the motive force to drive a crankshaft for providing power are referred to herein as primary power systems. In most primary power systems the efficiency of the system ranges from below 30% to a high of almost 50%. This means that the majority of energy contained in the fuel is lost in the form of heat to the atmosphere through either the cooling circuit or exhaust of the internal combustion engine.
However, the waste energy or exhaust gas from the internal combustion engine of a primary power system may be utilized as the energy input for a bottoming cycle power system. If enough useful work can be recovered from such a bottoming cycle power system, the bottoming cycle power system could then be used to supplement the output of the primary power system for a more efficient overall system output.
One type of bottoming cycle is known as an inverted Brayton cycle. The inverted Brayton cycle typically includes an expansion turbine that receives a flow of exhaust gas from a combustion process of an internal combustion engine. The exhaust gas carries a significant amount of energy. However the flow of exhaust gas is typically only at, or slightly above, atmospheric pressure. For example, the exhaust pressure may only a few pounds per square inch (psi) above atmospheric pressure. This makes recovering useful work difficult.
In the inverted Brayton cycle, the exhaust gas flows through an expansion turbine (or expander) where it typically exits the expander at below atmospheric pressures (or vacuum pressures). The vacuum pressures are caused by a compression turbine (or compressor), which is the final step in the inverted Brayton cycle. That is, the exhaust gas enters the compressor where it is pumped back to atmospheric pressure. The amount of energy recovered from an inverted Brayton cycle is the energy produced by the expander minus the energy consumed by the compressor. Therefore, the less work needed by the compressor to compress the expanded volume of exhaust gas the higher the net-work produced from the inverted Brayton cycle.
Various prior art cooling systems can be utilized to reduce the volume of exhaust gas prior to entering the compressor in an inverted Brayton cycle and therefore, reduce the amount of work required by the compressor to compress the exhaust gas. Problematically however, these cooling systems consume a significant amount of energy due to pumps and/or other energy consuming devices needed to circulate coolants through the cooling system.
Further, the exhaust gas of an internal combustion engine contains a significant amount of water vapor as a naturally occurring by-product of the combustion process. Problematically, the water vapor has a relatively high specific volume and mass, which causes an unwanted burden on the compression work of the compressor in the inverted Brayton cycle.
Accordingly, there is a need for an inverted Brayton bottoming cycle wherein the volume of flow of exhaust gas is significantly and efficiently reduced after exiting the expander and prior to entering the compressor. More specifically, there is a need to reduce the work required of the compressor in an inverted Brayton bottoming cycle power system to increase the overall efficiency of that bottoming cycle power system. Further there is a need to efficiently decrease the volume and mass of water vapor in a flow of exhaust gas prior to entering the compressor of an inverted Brayton bottoming cycle power system.